Power amplifier cell

ABSTRACT

A power amplifier cell comprising a first power amplifier, a second power amplifier and a balun. The balun comprises a first inductor and a second inductor that define a first transformer; and a third inductor and a fourth inductor that define a second transformer. The following: (i) a parasitic capacitance of the first power amplifier; (ii) a leakage inductance of the first transformer; and (iii) a capacitive coupling between the first inductor and the second inductor, contribute to a first impedance matching circuit for the first power amplifier. Also, the following (iv) a parasitic capacitance of the second power amplifier; (v) a leakage inductance of the second transformer; and (vi) a capacitive coupling between the third inductor and the fourth inductor, contribute to a second impedance matching circuit for the second power amplifier.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority under 35 U.S.C. § 119 of Europeanpatent application no. 17199444.5, filed Oct. 31, 2018 the contents ofwhich are incorporated by reference herein.

The present disclosure relates to power amplifier (PA) cells. Inparticular to PA cells that include transformers, wherein leakageinductances of the transformers are used to contribute to impedancematching circuits for associated power amplifiers.

According to a first aspect of the present disclosure there is provideda power amplifier cell comprising:

-   -   a first input terminal configured to receive a first balanced        input signal;    -   a second input terminal configured to receive a second balanced        input signal;    -   an output terminal;    -   a reference terminal;    -   a first power amplifier having:        -   a first PA input terminal connected to the first input            terminal;        -   a first PA output terminal;    -   a second power amplifier having:        -   a second PA input terminal connected to the second input            terminal;        -   a second PA output terminal;    -   a balun comprising:        -   a first balanced node connected to the first PA output            terminal;        -   a second balanced node connected to the second PA output            terminal;        -   an unbalanced node connected to the output terminal;        -   a first inductor with a first end and a second end, the            second end of the first inductor connected to the unbalanced            node;        -   a second inductor with a first end and a second end, wherein            the second inductor is inductively coupled to the first            inductor in order to define a first transformer, the first            end of the second inductor connected to the first balanced            node, and the second end of the second inductor connected to            the reference terminal;        -   a third inductor with a first end and a second end, wherein            the first end of the third inductor is connected to the            first end of the first inductor and the second end of the            third inductor is connected to the reference terminal;        -   a fourth inductor with a first end and a second end, wherein            the first end of the fourth inductor is connected to the            second balanced node, the fourth inductor is inductively            coupled to the third inductor in order to define a second            transformer, and the second end of the fourth inductor is            connected to the reference terminal;        -   a mutual-capacitor having a first terminal and a second            terminal, the first terminal of the mutual-capacitor            connected to the first end of the first inductor and the            first terminal of the mutual-capacitor further connected to            the first end of the third inductor, the second terminal of            the mutual-capacitor connected to the reference terminal;    -   wherein:        -   (i) a parasitic capacitance of the first power            amplifier; (ii) a leakage inductance of the first            transformer; and (iii) a capacitive coupling between the            first inductor and the second inductor, are configured to            contribute to a first impedance matching circuit for the            first power amplifier; and        -   (iv) a parasitic capacitance of the second power            amplifier; (v) a leakage inductance of the second            transformer; and (vi) a capacitive coupling between the            third inductor and the fourth inductor, are configured to            contribute to a second impedance matching circuit for the            second power amplifier.

By providing the impedance matching circuits in this way, the poweramplifier cell can make advantageous use of the leakage inductance fromthe transformers, especially where the inductors/coils of thetransformers are loosely coupled. That is, the leakage inductances canbe used to efficiently (in terms of the number of components requiredand power consumption) contribute to the impedance matching circuits.

In one or more embodiments, the first impedance matching circuit isconfigured to provide impedance matching between the first poweramplifier and the balun.

In one or more embodiments, the second impedance matching circuit isconfigured to provide impedance matching between second power amplifierand the balun.

In one or more embodiments, the inductive coupling of the first inductorto the second inductor has an inductive coupling factor of from 0.55 to0.75, and/or the inductive coupling of the third inductor to the fourthinductor has an inductive coupling factor of from 0.55 to 0.75.

In one or more embodiments, the leakage inductance of the firsttransformer is configured to provide sufficient inductance for the firstimpedance matching circuit without requiring additional components toprovide the inductive functionality of the first impedance matchingcircuit. Optionally, the leakage inductance of the second transformer isconfigured to provide sufficient inductance for the second impedancematching circuit without requiring additional components to provide theinductive functionality of the second impedance matching circuit.

In one or more embodiments, the first inductor comprises a first lumpedequivalent of a transmission line; and/or the second inductor comprisesa second lumped equivalent of a transmission line; and/or the thirdinductor comprises a third lumped equivalent of a transmission line;and/or the fourth inductor comprises a fourth lumped equivalent of atransmission line.

In one or more embodiments, the inductive coupling factor of the firstinductor to the second inductor is defined by the relative spatialarrangement of the first inductor with respect to the second inductor;and/or the inductive coupling factor of the third inductor to the fourthinductor is defined by the relative spatial arrangement of the thirdinductor with respect to the fourth inductor.

In one or more embodiments, the balun further comprises a first couplingcapacitor. The first coupling capacitor may comprise a first terminaland a second terminal, wherein: the first terminal of the first couplingcapacitor is connected to the first end of the first inductor; and thesecond terminal of the first coupling capacitor is connected to thefirst end of the second inductor.

In one or more embodiments, the balun further comprises a secondcoupling capacitor. The second coupling capacitor may comprise a firstterminal and a second terminal, wherein the first terminal of the secondcoupling capacitor is connected to the first end of the third inductor;and the second terminal of the second coupling capacitor is connected tothe first end of the fourth inductor.

In one or more embodiments, the balun further comprises a loadcapacitor. The load capacitor may comprise a first terminal and a secondterminal, wherein: the first terminal of the load capacitor is connectedto the second end of the first inductor; and the second terminal of theload capacitor is connected to the reference terminal.

In one or more embodiments, the balun further comprises a first blockingcapacitor. The first blocking capacitor may comprise a first terminaland a second terminal, wherein: the first terminal of the first blockingcapacitor is connected to the second end of the second inductor; and thesecond terminal of the first blocking capacitor is connected to thereference terminal.

In one or more embodiments, the balun further comprises a secondblocking capacitor. The second blocking capacitor may comprise a firstterminal and a second terminal, wherein: the first terminal of thesecond blocking capacitor is connected to the second end of the fourthinductor; and the second terminal of the second blocking capacitor isconnected to the reference terminal.

In one or more embodiments, the power amplifier cell further comprises:

-   -   a first reactive component having a first terminal and a second        terminal, wherein:        -   the first terminal of the first reactive component is            connected to the first PA output terminal; and        -   the second terminal of the first reactive component is            connected to the reference terminal; and/or    -   a second reactive component having a first terminal and a second        terminal, wherein:        -   the first terminal of the second reactive component is            connected to the second PA output terminal; and        -   the second terminal of the second reactive component is            connected to the reference terminal.

In one or more embodiments, the power amplifier cell further comprises:

-   -   a first harmonic-compensation-network connected to the second        inductor, the first harmonic-compensation-network comprising a        first compensation capacitor and a first compensation inductor;        and/or    -   a second harmonic-compensation-network connected to the fourth        inductor, the second harmonic-compensation-network comprising a        second compensation capacitor and a second compensation        inductor.

In one or more embodiments, the first harmonic-compensation-network isconnected to the second end of the second inductor, and/or the secondharmonic-compensation-network is connected to the second end of thefourth inductor.

In one or more embodiments, the first harmonic-compensation-network isconnected to the first end of the second inductor, and/or the secondharmonic-compensation-network is connected to the first end of thefourth inductor.

There may be provided a Doherty amplifier circuit, which comprises amain amplifier and a peaking amplifier, wherein the main amplifierand/or the peaking amplifier comprise any power amplifier cell disclosedherein.

While the disclosure is amenable to various modifications andalternative forms, specifics thereof have been shown by way of examplein the drawings and will be described in detail. It should beunderstood, however, that other embodiments, beyond the particularembodiments described, are possible as well. All modifications,equivalents, and alternative embodiments falling within the spirit andscope of the appended claims are covered as well.

The above discussion is not intended to represent every exampleembodiment or every implementation within the scope of the current orfuture Claim sets. The figures and Detailed Description that follow alsoexemplify various example embodiments. Various example embodiments maybe more completely understood in consideration of the following DetailedDescription in connection with the accompanying Drawings.

BRIEF DESCRIPTION OF DRAWINGS

One or more embodiments will now be described by way of example onlywith reference to the accompanying drawings in which:

FIG. 1 shows an example embodiment of a power amplifier (PA) cell;

FIG. 2 shows an even-mode equivalent circuit of the PA cell of FIG. 1,along with an associated Smith Chart;

FIG. 3 shows a simulated response for even-mode excitation to thecircuit of FIGS. 1 and 2;

FIG. 4 shows another example embodiment of a power amplifier (PA) cell,which includes a first harmonic-compensation-network and a secondharmonic-compensation-network;

FIG. 5 shows plots of the 2nd harmonic impedances that are presented tothe first and second PAs for the circuit of FIG. 4;

FIG. 6 shows plots of the base-band impedances that are presented to thefirst and second PAs for the circuit of FIG. 4;

FIG. 7 shows the results of odd-mode analysis of the reflectioncoefficient at a PA output terminal of the circuit of FIG. 1;

FIGS. 8a and 8b show two further examples embodiment of a poweramplifier (PA) cell, which include one or moreharmonic-compensation-networks;

FIG. 9 shows an example embodiment of a wideband PA circuit;

FIG. 10 shows plots of efficiency and impedance of the DPA shown in FIG.9; and

FIG. 11 shows an example of a wideband DPA with a combination ofon-chip/off-chip components.

Transmitters can include RF power amplifiers. The efficiency of such anRF power amplifier (PA) is important to the efficiency of thetransmitter. Moreover, it can be advantageous for the PA to be efficientover not only under maximum power conditions but also under powerbacked-off conditions. This can be addressed by using advanced PAconcepts for example Doherty, Outphasing and envelope tracking/envelopeelimination & restoration (ET/ERR) etc.

Simultaneous requirements on video & RF bandwidth, along with a desirefor a high average efficiency of the design, can make the design of thePA very complicated. For example, in order to work efficiently and atthe same time process wideband modulation signals, the PA can benefitfrom having low impedances at video frequencies, and also optimum loadat fundamental and second harmonic frequencies. In the case of widebandamplifiers, it can be extremely difficult (or impossible) to meet theabove stated requirements simultaneously. Moreover, if the PA cell is tobe used in wideband DPA (differential power amplifier) architecture, itmay also need to meet certain additional requirements such as: 1)precise 90 degree phase delay in front of a main PA (from an internalcurrent source) in a Doherty amplifier; 2) precise 180 degree phasedelay in front of a peaking PA (from an internal current source) in aDoherty amplifier; and 3) no (or only limited) impedance transformationbefore power combining in a Doherty amplifier.

A novel circuit will be described below, which uses differentialarchitecture. However rather than using very tightly coupledtransformers, examples of the novel circuit utilise weak couplingbetween coils to create an improved circuit for base-band, fundamentaland second harmonic frequencies. The weak coupling can result in leakageinductances that can be used to contribute to impedance matchingcircuits for amplifiers in the circuit, or for multi-segment lumpedequivalent of transmission lines to be used in in a DPA combiner (if thecircuit is used in a DPA configuration as will be discussed below).Embodiments of the circuit can advantageously generate impedances thathave a relatively constant value over a wideband frequency band, alongwith an option of moving the second harmonic impedances to very low orvery high conditions, thus providing the possibilities of either usingconventional class of operations of the PA devices or high efficiencyinverse class operation.

FIG. 1 shows an example embodiment of a power amplifier (PA) cell, whichcan be used in a transmitter for example.

The PA cell includes a first input terminal 103, a second input terminal105 and a reference terminal 140. The first input terminal 103 isconfigured to receive a first balanced input signal, and the secondinput terminal 105 is configured to receive a second balanced inputsignal. The PA cell also includes an output terminal 138, which isconfigured to provide an output-current (i_(x)) to a load (not shown).In this example, the reference terminal 140 is a ground terminal.

The PA cell includes a first power amplifier (Q1) 102 and a second poweramplifier (Q2) 104. In this example the power amplifiers are provided asBJTs. However, other types of transistors can be used, including MOS,CMOS, FETs, etc. As will be discussed below, the first power amplifier(Q1) 102 processes the first balanced input signal, and the second poweramplifier (Q2) 104 processes the second balanced input signal.

The first power amplifier (Q1) 102 has a first PA input terminal (inthis example the base of the transistor) that is connected to the firstinput terminal 103, and also has a first PA output terminal (in thisexample the collector of the transistor). Similarly, the second poweramplifier (Q2) 104 has a second PA input terminal (base) connected tothe second input terminal 105, and also has a second PA output terminal(collector).

The PA cell includes a balun 111, which has a first balanced node 107, asecond balanced node 109, and an unbalanced node 137. The unbalancednode 137 is connected to the output terminal 138. The first balancednode 107 is connected to the first PA output terminal (the collector ofQ1). The second balanced node is connected to the second PA outputterminal (the collector of Q2). In this way, the two power amplifiers(Q1, Q2) 102, 104 can be considered as a differential pair for excitingthe balun 111.

The balun 111 has a first inductor (L2) 118 with a first end and asecond end, and also has a second inductor (L1) 122 with a first end anda second end. The second inductor (L1) 122 is inductively coupled to thefirst inductor (L2) 118 in order to define a first transformer. Thesecond end of the first inductor (L2) 118 is connected to the unbalancednode 138. The first end of the second inductor (L1) 122 is connected tothe first balanced node 107. The second end of the second inductor (L1)122 is connected to the reference terminal 140, either directly orindirectly as shown in FIG. 1.

The balun 111 has a third inductor (L3) 120 with a first end and asecond end, and a fourth inductor (L4) 124 with a first end and a secondend. The fourth inductor (L4) 124 is inductively coupled to the thirdinductor (L3) 120 in order to define a second transformer. The first endof the third inductor (L3) 120 is connected to the first end of thefirst inductor (L2) 118. The second end of the third inductor (L3) 120is connected to the reference terminal 140. The first end of the fourthinductor (L4) 124 is connected to the second balanced node 109. Thesecond end of the fourth inductor (L4) 124 is connected to the referenceterminal 140, either directly or indirectly as shown in FIG. 1.

In this example, the balun 111 also includes a mutual-capacitor (Cm) 126having a first terminal and a second terminal. The first terminal of themutual-capacitor (Cm) 126 is connected to the first end of the firstinductor (L2) 118. The first terminal of the mutual-capacitor (Cm) 126is also connected to the first end of the third inductor (L3) 120. Thesecond terminal of the mutual-capacitor (Cm) 126 is connected to thereference terminal 140. This mutual-capacitor (Cm) 126 can form part ofan output matching network/lumped transmission lines in the case ofodd-mode/differential excitation.

Shown schematically in FIG. 1 is a leakage inductance 110 of the firsttransformer. This leakage inductance 110 can be considered as being inseries between the first PA output terminal (the collector of thetransistor, Q1) and the first balanced node 107. The value of theleakage inductance 110 is defined by the degree of inductive coupling ofthe first inductor (L2) 118 to the second inductor (L1) 122. In thisexample, the inductive coupling of the first inductor (L2) 118 to thesecond inductor (L1) 122 is relatively weak/loose and has an inductivecoupling factor of from 0.55 to 0.75. In other examples, it may bebetween less than 0.8, or less than 0.7. Using a relatively low couplingfactor is counter-intuitive because circuit designers usually designtransformers to have as high an inductive coupling factor as possible.

Similarly, FIG. 1 shows a leakage inductance 112 of the secondtransformer, in series between the second PA output terminal (thecollector of the transistor, Q2) and the second balanced node 109. Thevalue of the leakage inductance 112 of the second transformer can bedefined by an inductive coupling of the third inductor (L3) 120 to thefourth inductor (L4) 124, that is in one of the ranges discussed abovewith reference to the leakage inductance 110 of the first transformer.

The inductive coupling factor of the first inductor (L2) 118 to thesecond inductor (L1) 122 is defined by, amongst other things, therelative spatial arrangement of the first inductor (L2) 118 with respectto the second inductor (L1) 122; and the inductive coupling factor ofthe third inductor (L3) 120 to the fourth inductor (L4) 124 is definedby the relative spatial arrangement of the third inductor (L3) 120 withrespect to the fourth inductor (L4) 124.

As will be discussed below, the level of inductive coupling between thefirst inductor (L2) 118 and the second inductor (L1) 122, and betweenthe third inductor (L3) 120 and the fourth inductor (L4) 124, can be setsuch that the leakage inductances 110, 112 provide sufficient inductancefor respective impedance matching circuits without requiring additionalcomponents to provide the inductive functionality of the impedancematching circuit.

FIG. 1 shows that the balun 111 also comprises a first couplingcapacitor (C_(c)) 114 and a second coupling capacitor (C_(c)) 116. Thesecoupling capacitors 114, 116 may be provided by discrete capacitorcomponents, or the associated capacitances may be provided by theinherent capacitive coupling between the associated inductors (or anyother components or signal paths within the balun 111).

The first coupling capacitor (C_(c)) 114 has a first terminal and asecond terminal. The first terminal of the first coupling capacitor(C_(c)) 114 is connected to the first end of the first inductor (L2)118. The second terminal of the first coupling capacitor (C_(c)) 114 isconnected to the first end of the second inductor (L1) 122. The secondcoupling capacitor (C_(c)) 116 also has a first terminal and a secondterminal. The first terminal of the second coupling capacitor (C_(c))116 is connected to the first end of the third inductor (L3) 120. Thesecond terminal of the second coupling capacitor (C_(c)) 116 isconnected to the first end of the fourth inductor (L4) 124.

A parasitic capacitance of the first power amplifier (Q1) 102, isrepresented in FIG. 1 as a first device-capacitor 106. Similarly, aparasitic capacitance of the second power amplifier (Q2) 104, isrepresented in FIG. 1 as a second device-capacitor 108. Thedevice-capacitors 106, 108 are shown in series between: (i) theassociated PA output terminal (collector) of the power amplifier; and(ii) the reference terminal 140.

The following components of the PA cell can be considered ascontributing to an impedance matching circuit for the first poweramplifier (Q1) 102:

-   -   (i) the parasitic capacitance 106 of the first power amplifier        (Q1) 102;    -   (ii) the leakage inductance 110 of the first transformer; and    -   (iii) the capacitive coupling (C_(c)) 114 between the first        inductor (L2) 118 and the second inductor (L1) 122.

Similarly, the following components can be considered as contributing toan impedance matching circuit for the second power amplifier (Q2) 104:

-   -   (iv) the parasitic capacitance 108 of the second power amplifier        (Q2) 104;    -   (v) the leakage inductance 112 of the second transformer; and    -   (vi) the capacitive coupling (C_(c)) 116 between the third        inductor (L3) 120 and the fourth inductor (L4) 124.

In this way, the first impedance matching circuit can provide impedancematching between the first power amplifier (Q1) 102 and the balun 111.Similarly, the second impedance matching circuit can provide impedancematching between second power amplifier (Q2) 104 and the balun 111. Byproviding the impedance matching circuits in this way, the circuit canmake advantageous use of the leakage inductance from the transformers,especially where the inductors/coils of the transformers are looselycoupled. That is, the leakage inductances can be used to efficiently (interms of the number of components required and power consumption)contribute to the impedance matching circuits.

In some examples additional components may also be used for theimpedance matching circuits. For example, to increase or decrease thecapacitance of the parasitic capacitances 106, 108 and/or the capacitivecouplings (C_(c)) 114, 116.

For instance, additional reactive components can be provided in seriesbetween: (i) a PA output terminal (collector) of the or each poweramplifier (Q1, Q2) 102, 104; and (ii) the reference terminal 140. Inthis way, functionally they are in parallel with the associatedparasitic capacitance 106, 108 of the power amplifier (device-capacitor106). Use of such reactive components can be used to adjust theoperation of the impedance matching circuits, for example so that theycan be tuned to a specific application.

More specifically, a first reactive component (not shown) can be usedthat has a first terminal and a second terminal. The first terminal ofthe first reactive component can be connected to the first PA outputterminal (collector of Q1); and the second terminal of the firstreactive component can be connected to the reference terminal 140. Asecond reactive component (not shown) can be used that has a firstterminal and a second terminal. The first terminal of the secondreactive component can be connected to the second PA output terminal(collector of Q2). The second terminal of the second reactive componentcan be connected to the reference terminal 140.

In the example of FIG. 1, the balun 111 further comprises a firstblocking capacitor (C_(B)) 128 and a second blocking capacitor (C_(B))130. The first blocking capacitor (C_(B)) 128 has a first terminal and asecond terminal. The first terminal of the first blocking capacitor(C_(B)) 128 is connected to the second end of the second inductor (L1)122. The second terminal of the first blocking capacitor (C_(B)) 128 isconnected to the reference terminal 140. The second blocking capacitor(C_(B)) 130 also has a first terminal and a second terminal. The firstterminal of the second blocking capacitor (C_(B)) 130 is connected tothe second end of the fourth inductor (L4) 124. The second terminal ofthe second blocking capacitor (C_(B)) 130 is connected to the referenceterminal 140.

The blocking capacitors (C_(B)) 128, 130 can advantageously perform afunction of video decoupling, which can be beneficial for allowing widevideo bandwidths.

A node between the first blocking capacitor (C_(B)) 128 and the secondinductor (L1) 122 can be considered as a first-DC-feeding-node 134. Anode between the second blocking capacitor (C_(B)) 130 and the fourthinductor (L4) 124 can be considered as a second-DC-feeding-node 136. Aswill be discussed below, as part of the even-mode analysis these nodescan be used to feed DC to the power amplifiers (Q1, Q2) 102, 104.

FIG. 1 also shows that the balun 111 includes a load capacitor 132,which has a first terminal and a second terminal. The first terminal ofthe load capacitor 132 is connected to the second end of the firstinductor (L2) 118. The second terminal of the load capacitor 132 isconnected to the reference terminal 140. The load capacitor 132 can alsoform part of a matching circuit.

In some examples, one or more of the inductors (L2, L1, L3, L4) 118,122, 120, 124 can be implemented as a lumped equivalent of atransmission line. This can be a convenient way of implementing a planartransformer.

Even-Mode Analysis

FIG. 2 shows an even-mode equivalent circuit of the PA cell of FIG. 1,along with an associated Smith Chart 242. Components shown in FIG. 2 aregiven reference numbers in the 200 series, which correspond with thereference numbers of the same components in FIG. 1.

This even-mode analysis is valid for second harmonic as well asbase-band frequencies (as the base-band current drawn by the poweramplifiers 202, 204 depends on the magnitude of the RF voltages only).The voltages across the first-inductor (v_(x1)) and the third-inductor(v_(x2)) of FIG. 1 cancel each other, which is why the first-inductor(L2) and the third-inductor (L3) are not shown in FIG. 2. Therefore, theoutput-current (i_(x)) through the load is reduced to zero. Note thatthe blocking-capacitors (C_(B)) that are shown in FIG. 1 can be highvalue capacitors, and therefore they create an electrical short at thefundamental and as well as at second harmonic frequencies. This is whythey are not shown in FIG. 2.

As indicated above with reference to FIG. 1, the first-DC-feeding-node234 and the second-DC-feeding-node 236 can be used to feed DC to thepower amplifiers 202, 204.

FIG. 3 shows a simulated response for even-mode excitation to thecircuit of FIGS. 1 and 2. The plots show how the 2^(nd) harmonicimpedances are related to fundamental frequency. The Smith Chart on theright of FIG. 3 shows S(1,1), which is the input reflection coefficientat the device node (in FIG. 1 the device node is the collector of thePA) normalized to the optimum load of the PA device. FIG. 4 will be usedto describe how the second harmonic impedances can be adjusted by addingan uncoupled inductor/capacitor network in front of the PA devices.

FIG. 4 shows another example embodiment of a power amplifier (PA) cell.The PA cell of FIG. 4 is similar to that of FIG. 1, and correspondingcomponents have been given corresponding reference numbers in the 400series.

The PA cell of FIG. 4 includes a first harmonic-compensation-network 444and a second harmonic-compensation-network 446. The firstharmonic-compensation-network 444 is connected to the first end of thesecond inductor 422. In this example, the firstharmonic-compensation-network 444 is also connected to the outputterminal of the first PA 402. The second harmonic-compensation-network446 is connected to the first end of the fourth inductor 424. In thisexample, the second harmonic-compensation-network 446 is also connectedto PA output terminal of the second PA 404.

The first harmonic-compensation-network 444 in this example includes twocompensation capacitors 448, 452 and a first compensation inductor 450.The first compensation inductor 450 is connected in series between thesecond inductor 422 and the output terminal of the first PA 402. Eitherof the two compensation capacitors 448, 452 can be considered as a firstcompensation capacitor: in FIG. 4, one compensation capacitor 448 isconnected in series between (i) the output terminal of the first PA 402,and (ii) the reference terminal 440; and the other compensationcapacitor 452 is connected in series between (i) the first end of thesecond inductor 422, and (ii) the reference terminal 440.

The second harmonic-compensation-network 446 in this example alsoincludes two compensation capacitors 454, 458 and a second compensationinductor 456. Either of the two compensation capacitors 454, 458 can beconsidered as a second compensation capacitor. The second compensationinductor 456 is connected in series between the fourth inductor 424 andthe output terminal of the second PA 404. One of the compensationscapacitor 454 is connected in series between (i) the output terminal ofthe second PA 402, and (ii) the reference terminal 440; and the othercompensation capacitor 458 is connected in series between (i) the firstend of the fourth inductor 424, and (ii) the reference terminal 440.

Operation of the circuit of FIG. 4 at the video/baseband frequencies issimilar to the even-mode analysis shown in FIG. 2.

FIG. 5 shows plots of the 2^(nd) harmonic impedances that are presentedto the first and second PAs for the circuit of FIG. 4; that is thecircuit with the first and second harmonic-compensation-networks.

FIG. 6 shows plots of the base-band impedances that are presented to thefirst and second PAs for the circuit of FIG. 4. Note that the optimumload of the PA device used in this example circuit is 40 Ohm. Theimpedance is less than 10 times optimum load of the PA device over thefrequency range up-to 600 MHz, which would provide excellent performancefor wideband modulated signals.

Odd-Mode Analysis

In order to estimate the performance of the circuit of FIG. 1 forfundamental (differential signals), odd-mode analysis is applied to thecircuit of the FIG. 1. In this mode, the circuit can be considered as amulti-stage ladder network (not shown) to the output load. Such amulti-stage ladder network can provide very wideband bandwidth. This canbe because, in impedance matching, a multi-stage network provides widerbandwidth as the total impedance step is divided into smaller steps.

FIG. 7 shows the results of odd-mode analysis of the reflectioncoefficient at a PA output terminal (the collector of a PA transistor)of the circuit of FIG. 1). FIG. 7 shows that the input reflectioncoefficient (S11) at the collector of the PA devices (taking out theinternal collector capacitance) for the fundamental frequencies underodd-mode excitation conditions. The right-hand plot of FIG. 7 shows twocurves: a first curve 750 that represents the impedance seen by thefirst PA (which can be considered as a positive device), and a secondcurve 752 that represents the impedance seen by the second PA (which canbe considered as a negative device).

The right-hand plot of FIG. 7 also shows a line 754 at −25 dB. FIG. 7shows that the circuit of FIG. 1 advantageously provides a reflectioncoefficient that is better than −25 dB over more than 30% fractionalbandwidth.

FIGS. 8a and 8b show two further examples embodiment of a poweramplifier (PA) cell, which include one or moreharmonic-compensation-networks. The PA cells of FIGS. 8a and 8b aresimilar to that of FIG. 1, and corresponding components have been givencorresponding reference numbers in the 800 series. In these examples,the harmonic-compensation-networks can be for higher harmonics.Optionally, the leakage inductances (not shown) of the transformersand/or the blocking-capacitors (C_(B)) 828, 830; 828 a, 830 a (which mayalso be referred to as termination capacitances) can be embedded by theharmonic-compensation-networks.

The PA cell of FIG. 8a includes a first harmonic-compensation-network860 and a second harmonic-compensation-network 861. The firstharmonic-compensation-network 860 is connected to the second inductor822. More particularly, the first harmonic-compensation-network 860 isconnected in series between: (i) the second end of the second inductor822; and (ii) the reference terminal 840.

The first harmonic-compensation-network 860 in this example includes oneor more LC networks, wherein each LC network comprises a firstcompensation capacitor in parallel with a first compensation inductor.If only a single LC network 860 a is used, then the firstharmonic-compensation-network can be used for 3^(rd) harmonic matching.If two LC networks 860 b are used in series with each other, then thefirst harmonic-compensation-network can be used for 3^(rd) and 5^(th)harmonic matching. It will be appreciated that further LC networks canbe used in series with each other to provide matching for higher orderharmonics.

The second harmonic-compensation-network 861 can be implemented in anyof the ways described with reference to the firstharmonic-compensation-network 860, and is connected between the fourthinductor 824 and the reference terminal.

The PA cell of FIG. 8b includes a harmonic-compensation-network 862. Theharmonic-compensation-network 862 is connected to the first inductor818. More particularly, the harmonic-compensation-network 862 isconnected in series between: (i) the second end of the first inductor818; and (ii) the unbalanced node 838.

The harmonic-compensation-network 862 in this example includes one ormore LC networks 862 a, 862 b that can be similar to theharmonic-compensation-networks described with reference to FIG. 8 a.

FIG. 9 shows an example embodiment of a wideband PA circuit, whichincludes transmission line (TL) type delay properties with a delay ofless than 45 degrees. At the same time, it does not transform theimpedances, which makes its ideal to be used with wideband DPAarchitectures such as Doherty amplifiers.

FIG. 10 shows plots of efficiency and impedance of the DPA shown in FIG.9. FIG. 10 shows a simulated response with real PA devices (Qubic 8G).The lumped components used for generating the results of the FIG. 10 arelossless, and a realistic coupling factor of 0.65 has been used in thisexample. Such a coupling factor can be obtained by lateral coupling ofthe transformer coils/inductors.

The top plot of FIG. 10 represents the load seen by the main PA of theDPA at back-off power level, and shows that it is advantageouslywideband and is close to a real value (that is, with 0° phase) over thewideband.

FIG. 11 shows an example of a wideband DPA with a combination ofon-chip/off-chip components.

The wideband DPA architectures of FIG. 9 or FIG. 11 can be considered asDoherty amplifier circuits, which include a main amplifier and a peakingamplifier. Wherein the main amplifier and a peaking amplifier areprovided by a PA cell that is disclosed herein.

The wideband DPA architectures of FIG. 9 or FIG. 11 can be implementedwith on-chip lumped components or a combination of on-chip/off-chipcomponents.

The instructions and/or flowchart steps in the above figures can beexecuted in any order, unless a specific order is explicitly stated.Also, those skilled in the art will recognize that while one example setof instructions/method has been discussed, the material in thisspecification can be combined in a variety of ways to yield otherexamples as well, and are to be understood within a context provided bythis detailed description.

In some example embodiments the set of instructions/method stepsdescribed above are implemented as functional and software instructionsembodied as a set of executable instructions which are effected on acomputer or machine which is programmed with and controlled by saidexecutable instructions. Such instructions are loaded for execution on aprocessor (such as one or more CPUs). The term processor includesmicroprocessors, microcontrollers, processor modules or subsystems(including one or more microprocessors or microcontrollers), or othercontrol or computing devices. A processor can refer to a singlecomponent or to plural components.

In other examples, the set of instructions/methods illustrated hereinand data and instructions associated therewith are stored in respectivestorage devices, which are implemented as one or more non-transientmachine or computer-readable or computer-usable storage media ormediums. Such computer-readable or computer usable storage medium ormedia is (are) considered to be part of an article (or article ofmanufacture). An article or article of manufacture can refer to anymanufactured single component or multiple components. The non-transientmachine or computer usable media or mediums as defined herein excludessignals, but such media or mediums may be capable of receiving andprocessing information from signals and/or other transient mediums.

Example embodiments of the material discussed in this specification canbe implemented in whole or in part through network, computer, or databased devices and/or services. These may include cloud, internet,intranet, mobile, desktop, processor, look-up table, microcontroller,consumer equipment, infrastructure, or other enabling devices andservices. As may be used herein and in the claims, the followingnon-exclusive definitions are provided.

In one example, one or more instructions or steps discussed herein areautomated. The terms automated or automatically (and like variationsthereof) mean controlled operation of an apparatus, system, and/orprocess using computers and/or mechanical/electrical devices without thenecessity of human intervention, observation, effort and/or decision.

It will be appreciated that any components said to be coupled may becoupled or connected either directly or indirectly. In the case ofindirect coupling, additional components may be located between the twocomponents that are said to be coupled.

In this specification, example embodiments have been presented in termsof a selected set of details. However, a person of ordinary skill in theart would understand that many other example embodiments may bepracticed which include a different selected set of these details. It isintended that the following claims cover all possible exampleembodiments.

1. A power amplifier cell comprising: a first input terminal configuredto receive a first balanced input signal; a second input terminalconfigured to receive a second balanced input signal; an outputterminal; a reference terminal; a first power amplifier having: a firstPA input terminal connected to the first input terminal; a first PAoutput terminal; a second power amplifier having: a second PA inputterminal connected to the second input terminal; a second PA outputterminal; a balun comprising: a first balanced node connected to thefirst PA output terminal; a second balanced node connected to the secondPA output terminal; an unbalanced node connected to the output terminal;a first inductor with a first end and a second end, the second end ofthe first inductor connected to the unbalanced node; a second inductorwith a first end and a second end, wherein the second inductor isinductively coupled to the first inductor in order to define a firsttransformer, the first end of the second inductor connected to the firstbalanced node, and the second end of the second inductor connected tothe reference terminal; a third inductor with a first end and a secondend, wherein the first end of the third inductor is connected to thefirst end of the first inductor and the second end of the third inductoris connected to the reference terminal; a fourth inductor with a firstend and a second end, wherein the first end of the fourth inductor isconnected to the second balanced node, the fourth inductor isinductively coupled to the third inductor in order to define a secondtransformer, and the second end of the fourth inductor is connected tothe reference terminal; a mutual-capacitor having a first terminal and asecond terminal, the first terminal of the mutual-capacitor connected tothe first end of the first inductor and the first terminal of themutual-capacitor further connected to the first end of the thirdinductor, the second terminal of the mutual-capacitor connected to thereference terminal; wherein: (i) a parasitic capacitance of the firstpower amplifier; (ii) a leakage inductance of the first transformer; and(iii) a capacitive coupling between the first inductor and the secondinductor, are configured to contribute to a first impedance matchingcircuit for the first power amplifier; and (iv) a parasitic capacitanceof the second power amplifier; (v) a leakage inductance of the secondtransformer; and (vi) a capacitive coupling between the third inductorand the fourth inductor, are configured to contribute to a secondimpedance matching circuit for the second power amplifier.
 2. The poweramplifier cell of claim 1, wherein the first impedance matching circuitis configured to provide impedance matching between the first poweramplifier and the balun.
 3. The power amplifier cell of claim 1, whereinthe second impedance matching circuit is configured to provide impedancematching between second power amplifier and the balun.
 4. The poweramplifier cell of claim 1 wherein the inductive coupling of the firstinductor to the second inductor has an inductive coupling factor of from0.55 to 0.75, and the inductive coupling of the third inductor to thefourth inductor has an inductive coupling factor of from 0.55 to 0.75.5. The power amplifier cell of claim 1, wherein: the leakage inductanceof the first transformer is configured to provide sufficient inductancefor the first impedance matching circuit without requiring additionalcomponents to provide the inductive functionality of the first impedancematching circuit; and the leakage inductance of the second transformeris configured to provide sufficient inductance for the second impedancematching circuit without requiring additional components to provide theinductive functionality of the second impedance matching circuit.
 6. Thepower amplifier cell of claim 1, wherein: the first inductor comprises afirst lumped equivalent of a transmission line; the second inductorcomprises a second lumped equivalent of a transmission line; the thirdinductor comprises a third lumped equivalent of a transmission line; andthe fourth inductor comprises a fourth lumped equivalent of atransmission line.
 7. The power amplifier cell of claim 1, wherein: theinductive coupling factor of the first inductor to the second inductoris defined by the relative spatial arrangement of the first inductorwith respect to the second inductor; and the inductive coupling factorof the third inductor to the fourth inductor is defined by the relativespatial arrangement of the third inductor with respect to the fourthinductor.
 8. The power amplifier cell of claim 1, wherein the balunfurther comprises: a first coupling capacitor comprising a firstterminal and a second terminal, wherein: the first terminal of the firstcoupling capacitor is connected to the first end of the first inductor;and the second terminal of the first coupling capacitor is connected tothe first end of the second inductor; and a second coupling capacitorcomprising a first terminal and a second terminal; the first terminal ofthe second coupling capacitor is connected to the first end of the thirdinductor; and the second terminal of the second coupling capacitor isconnected to the first end of the fourth inductor.
 9. The poweramplifier cell of claim 1, wherein the balun further comprises a loadcapacitor comprising a first terminal and a second terminal, wherein:the first terminal of the load capacitor is connected to the second endof the first inductor; and the second terminal of the load capacitor isconnected to the reference terminal.
 10. The power amplifier cell ofclaim 1, wherein the balun further comprises: a first blocking capacitorcomprising a first terminal and a second terminal, wherein: the firstterminal of the first blocking capacitor is connected to the second endof the second inductor; and the second terminal of the first blockingcapacitor is connected to the reference terminal; and a second blockingcapacitor comprising a first terminal and a second terminal, wherein:the first terminal of the second blocking capacitor is connected to thesecond end of the fourth inductor; and the second terminal of the secondblocking capacitor is connected to the reference terminal.
 11. The poweramplifier cell of claim 1, further comprising: a first reactivecomponent having a first terminal and a second terminal, wherein: thefirst terminal of the first reactive component is connected to the firstPA output terminal; and the second terminal of the first reactivecomponent is connected to the reference terminal; and a second reactivecomponent having a first terminal and a second terminal, wherein: thefirst terminal of the second reactive component is connected to thesecond PA output terminal; and the second terminal of the secondreactive component is connected to the reference terminal.
 12. The poweramplifier cell of claim 1, further comprising: a firstharmonic-compensation-network connected to the second inductor, thefirst harmonic-compensation-network comprising a first compensationcapacitor and a first compensation inductor; and a secondharmonic-compensation-network connected to the fourth inductor, thesecond harmonic-compensation-network comprising a second compensationcapacitor and a second compensation inductor.
 13. The power amplifiercell of claim 12, wherein: the first harmonic-compensation-network isconnected to the second end of the second inductor; and the secondharmonic-compensation-network is connected to the second end of thefourth inductor.
 14. The power amplifier cell of claim 12, wherein: thefirst harmonic-compensation-network is connected to the first end of thesecond inductor; and the second harmonic-compensation-network isconnected to the first end of the fourth inductor.
 15. A Dohertyamplifier circuit, which comprises a main amplifier and a peakingamplifier, wherein the main amplifier and the peaking amplifier comprisea power amplifier cell of claim 1.